The magnetic recording media used on an information processing apparatus are indispensable as a recording-reproducing element and are widely used. What is required of this type of recording media include higher levels of electromagnetic conversion characteristics that are correctly reproduced; large recording capacity of higher density; appropriate composition properties that ensures good traveling operation, durability, and longer life; lower price; and trouble-free manufacturing process. To satisfy these requirements, various technical efforts have been exerted.
To sum up, the objective of these technical efforts is essentially development of high performance magnetic media comprising fine particles of good electromagnetic performance, wherein individual particles are totally independent of others to ensure good dispersibility and good dispersion stability, and the media in the form of final product is free from troubles and has good durability.
Using fine ferromagnetic powder of a good S/N ratio and large specific surface area, however, results in problems such as magnetic particles insufficiently dispersed in a binder, and a viscous magnetic paint. These problems in turn jeopardize the surface smoothness, durability, and magnetic characteristics of the magnetic layer, imposing difficulties in providing high performance magnetic recording media.
Additionally, in regards with dispersibility of the magnetic powder, studies have been focused both on a dispersion agent and binder.
Such magnetic recording media also incurs various problems in production techniques.
First, finer magnetic particles, and finer fillers such as Carbon Black powder result in decreased dispersibility, incurring many steps and longer time for a dispersion process, imposing an unsolved bottleneck in production technique.
Second, the viscosity stability of the magnetic pain during standing is poor, making it difficult to positively form a uniformly thick coat as a magnetic layer. This in turn makes it mandatory to add, as a thinner, a large amount of a solvent, or a fatty acid, phosphoric ester or the like, causing cost increase, troubles by a residual solvent, loss in the Young's modulus, and, as a result, the recording medium is subject to jeopardized traveling characteristics, damages on edges, loss in RF output level, and jitter fluctuation.
The magnetic recording medium having been provided with structural layers such as a magnetic layer is subjected to a curing process at 50.degree. to 70.degree. C. for 24 to 48 hours in order to stabilize performance and properties, and to ensure conformity to quality standards. However, excessive smoothness on the medium surface results in syneresis of a solvent and additives, jeopardizing the traveling characteristics of the medium.
To solve the above productivity problems, not only improvements in additives and manufacturing apparatuses but also magnetic powder and binder that are indispensable and various thermosetting resins such as polyurethane, cellulose, vinyl chloride resins and phenoxy resins; various resins modified by introduction of a polar group; various resins whose properties modified by an introduced polar group; and thermoplastic resins of unique behavior. These are combined in good compatibility so that the properties of the structural layers on the magnetic recording medium have been significantly improved, and, at the same time, the dispersibility and deposition of the magnetic powder, filler and the like have been positively improved. These improvements, however, are still insufficient.
The studies on magnetic powder have been hitherto centered principally on electromagnetic conversion characteristics, and have lacked in the viewpoints mentioned above, though a few studies centered on pretreatment of magnetic powder using a dispersing agent, and examples where less than 0.1 wt% Si is added to magnetic powder incidentally suggest the solution to the problems. In other words, it is no exaggeration to say that conventional studies totally ignore possibility of treating the surface or inside of individual magnetic particles.